I have a few hundred parts with a custom property called "assemblydoc"

They are all in the same folder.

The first part of the custom property, is a project number, the rest is unique for each part.

They have been copied to a new project, so I would like to change the firs part, but keep the second part.

Their content is a bit like this:

Part_1 assemblydoc = 1981-FAX001

Part_2 assemblydoc = 1981-FAY001

Part_3 assemblydoc = 1981-FAC002

Part_4 assemblydoc = 1981-FAB333

etc

I would like to change it to something like this:

Part_1 assemblydoc = 2001-FAX001

Part_2 assemblydoc = 2001-FAY001

Part_3 assemblydoc = 2001-FAC002

Part_4 assemblydoc = 2001-FAB333

etc

Any help would be appreciated.